Here is a Reddit post
Reddit Post | [Archive.org link in case of linkrot]
In short:
"If you buy bagged lettuce or salads, choose the bag that is the flattest. When the greens are packaged, all of the air is sucked out of the bag. Then as they age, they give off gas, making the bag puffier. Choose the flattest bag and your salad will be fresher, and last longer in the fridge."
It seems like a simple little tip! When you read it it comes off as something helpful and you may even be thinking you'll give it a try the next time you get groceries.
The issue is that it is 100% wrong. Salad bags are NOT emptied. In fact, they have a special gas mix pumped in to keep them fresh. The "puffiness" of the bag will have no affect on the freshness of the salad.
You may think this is a minor issue but as I said above - you were probably thinking (at least, many people were) of using this very technique to make your choice in the future. This could have pretty big effects if done by enough people.
If you look at the comments, the current top ones I see are:
"My wife always chooses the flatter ones, but her reasoning was she had better luck with the flatter ones. So this is explains her "good luck" with the flatter ones. Now I know. I will share this science with her!"
and
"a good LPT... I'm... I need a moment. Thank you."
and
"Exact opposite of what I’ve been doing; legit tip!!"
To make the comment they had to click a few times and type in their comment. If they had clicked their address bar and types in a question in Google they would have found this:
An actual source | [Archive.org link in case of linkrot]
What's she's talking about in detail | [Archive.org link in case of linkrot]
And even a NyTimes Article on it | [Archive.org link in case of linkrot]
Which is the actual answer. Same amount of work, but would have gotten a true answer.
That post has over 5000 upvotes and hundreds of comments, all just assuming it is true.
"Same. I always thought they inserted air, the way they do with bags of chips, to make sure the content isn't crushed. Guess I was wrong."
is a comment. They had their idea changed. While their idea was wrong, the new idea they have is also wrong. They still haven't taken the time to verify it.
This is a serious problem that we need to face online - a culture of fact checking needs to be pushed, even for small things like this.
Imagine the power of a wrong fact that adheres to your ideals on politics? Or one that sounds like the kind of thing someone you hate would say.
If people can't fact check something that doesn't attack any preconcieved notion, how can we expect people to fact check when there is a preconcieved notion.